Turbine abradable layer with progressive wear zone having a frangible or pixelated nib surface

Abstract

Turbine and compressor casing abradable component embodiments for turbine engines, with composite grooves and vertically projecting rows of ridges in planform patterns, establishing upper and lower wear zones. The lower wear zone reduces, redirects and/or blocks blade tip downstream airflow leakage, while the upper wear zone is optimized to minimize blade tip gap and wear by being more easily abradable than the lower zone. An elongated first ridge in the lower wear zone terminates in a continuous surface plateau. A plurality of second ridges or nibs, separated by grooves, project from the plateau, forming the upper wear zone. Each of the second ridges has a planform cross section smaller than the plateau planform cross section and a height smaller than the first ridge height. Some embodiments of the second ridges have spacing, planform cross sections, heights and separating groove dimensions selected for shearing when contacted by turbine blade tips.